First Peek with JWST/NIRCam Wide-field Slitless Spectroscopy: Serendipitous Discovery of a Strong [O iii]/H α Emitter at z = 6.11

Journal
Date Issued
2022
Author(s)
Sun, Fengwu
•
Egami, Eiichi
•
Pirzkal, Nor
•
Rieke, Marcia
•
Boyer, Martha
•
•
Gennaro, Mario
•
Girard, Julien
•
Greene, Thomas P.
•
Kelly, Doug
•
Koekemoer, Anton M.
•
Leisenring, Jarron
•
Misselt, Karl
•
Nikolov, Nikolay
•
Roellig, Thomas L.
•
Stansberry, John
•
Williams, Christina C.
•
Willmer, Christopher N.A.
DOI
Abstract
We report the serendipitous discovery of an [O iii] λ λ4959/5007 and Hα line emitter in the Epoch of Reionization (EoR) with the James Webb Space Telescope (JWST) commissioning data taken in the NIRCam wide-field slitless spectroscopy (WFSS) mode. Located 1/455″ away from the flux calibrator P330-E, this galaxy exhibits bright [O iii] λ λ4959/5007 and Hα lines detected at 3.7σ, 9.9σ, and 5.7σ, respectively, with a spectroscopic redshift of z = 6.112 ± 0.001. The total Hβ+[O iii] equivalent width is 664 ± 98 Å (454 ± 78 Å from the [O iii] λ5007 line). This provides direct spectroscopic evidence for the presence of strong rest-frame optical lines (Hβ+[O iii] and Hα) in EoR galaxies as inferred previously from the analyses of the Spitzer/IRAC spectral energy distributions (SEDs). Two spatial and velocity components are identified in this source, possibly indicating that this system is undergoing a major merger, which might have triggered the ongoing starburst with strong nebular emission lines over a timescale of 1/42 Myr, as our SED modeling suggests. The tentative detection of He ii λ4686 line (1.9σ), if real, may indicate the existence of very young and metal-poor star-forming regions with a hard UV radiation field. Finally, this discovery demonstrates the power and readiness of the JWST/NIRCam WFSS mode, and marks the beginning of a new era for extragalactic astronomy, in which EoR galaxies can be routinely discovered via blind slitless spectroscopy through the detection of rest-frame optical emission lines.
Volume
936
Issue
1
Start page
L8
Uri
Url
Issn Identifier
2041-8205
Rights
open.access
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